Tuning the Coordination Geometry and Magnetic Relaxation of Co(II) Single-Ion Magnets by Varying the Ligand Substitutions

Three mononuclear Co(II) complexes with the formulas of [Co(L 1 ) 2 ] ( 1 ), [Co(L 2 ) 2 (CH 3 OH) 2 ] ( 2 ), and [Co(L 3 ) 2 (CH 3 OH) 2 ] ( 3 ) (HL 1 = 4-nitro-2-(( E )- (propylimino)methyl)phenol, HL 2 = 2,4-dinitro-6-(( E )-(propylimino) methyl)phenol, HL 3 = 2-(methoxymethyl)-4-nitro-6-(( E )-(propylimino)methyl)phenol) have been synthesized and structurally characterized. The -CH 2 OCH 3 group in the ligand of complex 3 was in situ formed during the reaction. The Co(II) ion of complex 1 is in a distorted tetrahedral environment, while the Co(II) centers in complexes 2 and 3 adopt a deformed octahedral geometry. The static magnetic data can be well fitted by the spin ( 1 ) or Griffith-Figgis ( 2 and 3 ) Hamiltonian and negative D and B 2 0 values were obtained. Quantum chemical calculations confirm the presence of significant easy-axial magnetic anisotropy with non-negligible transversal contributions in all the three complexes. All the three complexes show field-induced slow magnetic relaxation with one ( 2 ) or two ( 1 and 3 ) relaxation processes. Interestingly, their coordination geometry and magnetic relaxation behaviors can be tuned by ligand substitutions.